Capacitive pointing stick apparatus for symbol manipulation in a graphical user interface

ABSTRACT

A structure is provided for a user-manipulable input device, such as an in-keyboard, joystick-type device, for allowing a user to provide input to a computer graphical user interface (GUI). The structure includes a user-manipulable, articulating member, and a plurality of stationary, electrically conductive sensors. The articulating member also has an electrically conductive member. The physical disposition of the articulating member and the sensors provides narrow gaps, across which are measurable capacitances. As the user manipulates the articulating member, the capacitances change in value. Circuitry produces signals related to the capacitances, and the signals are processed, according to a transfer function, to generate GU I input signals. The sensors are preferably sensing electrodes, incorporated into a circuit board. The articulating member is preferably a cone-shaped member, having a conductive surface which faces the sensors. The articulating member is mechanically coupled to the board holding the sensors by a flexing member that biases the articulating member to a quiescent position.

FIELD OF THE INVENTION

The invention generally relates to the field of computer graphical userinterface systems. More particularly, the invention relates touser-manipulable apparatus for moving a symbol, such as a cursor, on adisplay, and for entering “point and click” type user commands.

The invention has particular applicability to computer graphical userinterface (GUI) apparatus, and can be used in systems whichconventionally employ devices such as IBM Corporation's TrackPoint IIIpointing devices, in keyboards of various IBM computer products. (IBMand TrackPoint III are registered trademarks of International BusinessMachines Corporation.)

BACKGROUND OF THE INVENTION

The growing interactiveness of home entertainment systems, particularlycable television, interactive television, and Internet set-top boxes, isplacing greater demands on hand-operated controls.

Mice have been commonly used as user-manipulable GUI apparatus. Using amouse, a user directs the movement of a cursor across a display screenby corresponding manual mouse movements.

Joystick-type devices have also been used. In particular, IBMCorporation's TrackPoint III pointing device (hereinafter“TrackPoint-type device” or “TrackPoint device”) has been mountedin-keyboard in many laptop computers. A TrackPoint-type device includesa button-like structure resembling a pencil eraser and disposed betweenkeys of a computer keyboard, has facilitated the use of graphical userinterfaces (GUIs) in portable computers. The need for a mouse, and aflat working surface on which the user manipulates the mouse, iseliminated, because the user is able to manipulate the TrackPoint deviceentirely within the keyboard.

A conventional physical implementation of the TrackPoint III pointingdevice is described in co-pending, co-assigned U.S. patent applicationSer. No. 08/181,648, filed Jan. 4, 1994. That implementation includesstrain gauge sensors, and a post serving as a lever arm. By manipulatingthe post, the user flexes the strain gauges. Small analog signalsproduced by the strain gauges are interpreted by on-board software, andthe cursor is moved accordingly.

The strain gauges produce a ½% full-scale signal change, and must beindividually trimmed during manufacture to match their outputs. Themanufacturing and trimming of the strain gauges, combined with the smallanalog signal they produce, contribute to the cost of the sensor, and ofthe electronics required to make a TrackPoint III system. Moreover, thesmall full-scale magnitude of the signal change places a burden on thedata acquisition system which processes the strain gauge signals intocursor movement signals.

Therefore, an important objective in the design and manufacture ofTrackPoint type devices is the reduction of these cost-adding factors.

These issues have been confronted in the design and manufacture of othertypes of user-manipulable electronic components. For instance, aconventional structure is taught in Hughes, U.S. Pat. No. 4,305,007,“Electronic Two Directional Control Apparatus”, issued Dec. 8, 1981.This patent describes a structure including four sensing electrodes,whose capacitances independently vary in response to the proximity of anexternal object.

A physical implementation of the Hughes structure is shown in FIG. 7 ofthe Hughes patent, which is reproduced as FIG. 1 of the present patentapplication. For simplicity, and to allow for a brief summary of thedescription of the Hughes structure, the reference numbers not directlypertinent to the summary have been deleted.

The Hughes structure includes sensing electrodes 5 that map out fourquadrants. A controlling member 3 at the end of a displaceable member 2,supported from above by a ball joint 1, moves in relation to the sensingelectrodes 5. These elements are contained within a three dimensionalgrounded shield box 4.

Note, however, that, in addition to being impractical for implementationin a keyboard or in a portable computer, the Hughes structure requiresconsiderable cost for parts and assembly. Also, the manufacturingprocess must include manual trimming of the electronic circuit to matchthe outputs of the four quadrants. Therefore, the Hughes apparatus doesnot provide the desired low cost.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide cost reductionsin the manufacture of TrackPoint-type user-manipulable pointing deviceswhich had not been realized in conventional structures.

To achieve this and other objects, there is provided in accordance withthe invention an apparatus for sensing manipulation by a user and forproducing signals related to the manipulation. The signals produced bysuch an apparatus may then be used as part of a user interface system.For instance, the signals might be used in a personal computer having adisplay screen, for causing movement of a displayed symbol, such as acursor.

The apparatus essentially has two components. The first componentincludes an articulating member. Means are provided for causing thearticulating member to articulate responsive to user manipulationthereof, and thereafter, to return to a quiescent position.

The second component includes a sensor array, made up of a plurality ofsensing members disposed about the articulating member. Means areprovided for detecting respective signals from the sensing members, therespective signals varying in value depending on articulation of thearticulating member.

In accordance with the invention, these components are made up ofinexpensive electrical components and simple mechanical components, toproduce a low cost pointing device whose physical size and dimensionsare suited for use in applications such as in-keyboard TrackPoint-typedevices.

The sensing members preferably include flat, electrically conductivemembers on a planar substrate, such as etched conductive regions on aprinted circuit board, and the articulating member includes anelectrically conductive member whose varying proximity to the sensingmembers, due to the manipulation by the user, produces a correspondinglyvarying capacitance value. The magnitude of the capacitance isdetermined by a data acquisition system, preferably including RCoscillators and a microcontroller. In accordance with a suitabletransfer function, the capacitance value is used to produce the cursormovement signals.

A device according to the invention may advantageously be employed as apointing device for hand-held remote control applications, as well asfor keyboards. Cost is a driving factor in the success of any devicetargeted to the consumer electronics market. The capacitive sensor anddata acquisition system according to the invention (oscillator andmicrocontroller) provide advantageously low manufacturing costs.

The low-cost capacitive device according to the invention is alsoinherently less expensive than a mouse. Both pointing technologiesrequire a microcontroller. In addition, a mouse requires two opticalinterrupters, two mechanical disks, a rotating ball, and a threedimensional structure to align these items. A preferred implementationof the capacitive sensor-based device according to the inventionincludes a conductive disk attached to the circuit board, and aninexpensive integrated circuit (Schmitt Trigger NAND). The inventionuses fewer components, and is easier to manufacture and assemble. Theabsence of moving parts exposed to the environment means the inventionhas advantageously low maintenance, and a low failure rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional diagram of a prior art structure.

FIG. 2 is a side cross-section view of a first preferred embodiment ofthe invention.

FIG. 3 is a top view of a portion of the embodiment of FIG. 2, showingthe geometry of a set of sensing electrodes.

FIG. 4 is an electrical schematic diagram of circuitry for theembodiment of FIG. 2.

FIGS. 5 and 6 are cross-sectional diagrams showing views of variousalternative embodiments of a physical structure according to theinvention, further including switching for providing tactile feedback.

FIG. 7A is a cross-sectional diagram showing another preferredembodiment of the invention.

FIGS. 7B and 7C are detailed views of a portion of the embodiment ofFIG. 7A.

FIG. 8A is a side cross-sectional view of yet another preferredembodiment of the invention.

FIG. 8B is a top cross-sectional view of a portion of the embodiment ofFIG. 8A.

FIG. 9 is a graph showing transfer functions which relate manipulationforce input, sensor frequency output, and calibrated sensor output, forcalibration of an apparatus according to the invention.

FIGS. 10A and 10B are top views of sensing electrodes, similar to thatof FIG. 3, but showing alternative geometries.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The description which follows will generally presume that an apparatusaccording to the invention will be used in connection with a computer'suser interface. However, it will be understood that televisions,specialized World Wide Web browsers for use with televisions or otherhome electronics, and other such electronic devices, may also makeadvantageous use of the invention.

First Embodiment

Basic Sensing Device

A preferred embodiment of the invention is shown in FIGS. 2, 3, and 4.

FIG. 2 is a cross-sectional side view of a preferred embodiment of theinvention. An articulating member 20 includes a conductive cone 22coupled to a shaft 24 with a textured cap 26. An example of the cap maybe found in co-pending, co-assigned U.S. patent application Ser. No.08/315,651, filed Sep. 30, 1994, “Grip Cap for Computer Control Stick.”.The articulating member 20 produces a user-manipulable pointing stickdevice, having a look and feel similar to that of a conventionalTrackPoint III device.

In an alternative embodiment, however, the shaft 24 and textured cap 26can be replaced by a flat disk, which is pressed by the user.

The conductive cone 22 is preferably conical in shape, but conductivemembers of other shapes which would suggest themselves to personsskilled in the art for carrying out the invention may also be used.Also, a non-conductive member having a conductive layer, or member, onits surface, may also be used.

Underneath the conductive cone 22 is a circuit board 28, bearing aplurality of sensors, shown as sensing electrodes 30. The number ofsensing electrodes 30 is preferably four, for detection of bidirectionalmovement in two dimensions. However, other suitable numbers andarrangements of sensing electrodes 30 will be understood by personsskilled in the art as being suitable for other applications of theinvention.

FIG. 3 provides atop view of the board 28, showing in detail a preferredlayout of the sensing electrodes 30. The sensing electrodes 30 arearranged as four quadrants of a circle. The sensing electrodes 30 arepreferably etched copper clad, and electrically isolated from theconductive cone by a thin insulating layer, such as a solder mask ornon-conductive tape (not shown).

Referring back to FIG. 2, the articulating member 20 is mechanicallycoupled to the board 28 by means for biasing the articulating member 20to a quiescent position, from which the articulating member 20 ismovable by user manipulation. Gaps 33 appear between the conductive cone22 and the electrodes 30. The conical shape of the conductive cone 22facilitates the formation of the gaps 33. From the discussion whichfollows, it will be seen that other shapes, so long as the shapesfacilitate the formation of gaps, may equivalently be used.

In a preferred embodiment, the means for biasing includes a flexingmember, for biasing the conductive cone 22 to a quiescent position, andfor urging the conductive cone 22 back to the quiescent position if ithas been moved, by externally applied force, from the quiescentposition. The flexing member may be a tensile member such as a wire 32,which is coupled to the articulating member 20, and which runs down tothe board 28, to which the wire 32 is secured.

Because of the conical shape of the conductive cone 22, the apex of thecone 22 forms a point of contact between the articulating member 20 andthe board 28. The wire 32 runs axially through the conductive cone 22,emerges from the conductive cone 22 at its apex, and runs directlythrough the board 28. In the illustrated embodiment, the wire 32 issecured, by an electrically grounded securing rivet 34, to a conductiveground pad 36 on the bottom of the board 28.

The apex provides a pivoting point for the conductive cone 22. Tensionon the wire 32 provides spring action to maintain the articulatingmember 20 in an upright (i.e., quiescent) position when no force isexerted on the articulating member 20, and to return the articulatingmember 20 to the quiescent position after force, previously applied, isreleased.

When a force, normal to the shaft 24 (i.e., horizontal as shown in FIG.2), is applied, the wire 32 flexes, bringing a portion of the conductivecone 22 closer to one or more of the sensing electrodes 30, and anotherportion (on the opposite side) further away from the opposing one ormore sensing electrodes 30. The gaps 33 change dimensions, accordingly.

The conductive cone 22, the respective sensing electrodes 30, and thegaps therebetween create four variable capacitors. The values of thevariable capacitors depend on the distance between the conductive cone22 and the respective sensing electrodes 30, i.e., on the dimensions ofthe gaps 33. For instance, as the distance between the conductive cone22 and one of the sensing electrodes 30 decreases (that is, the width ofthe gap 33 decreases), the capacitance between the conductive cone 22and that one of the sensing electrodes 30 increases.

The arrangement of the four sensing electrodes 30, as per theillustrated preferred embodiment, is referred to as a quadraturedetection arrangement. Quadrature detection allows two degrees offreedom (i.e., the x and y components of applied force) to be measured.

The wire 32, which is grounded to the ground pad 36, preferably alsogrounds the conductive cone 22. The conductive ground pad 36 and thegrounded conductive cone 22 shield the sensing electrodes 30 fromelectrical noise and stray capacitance that might otherwise effectsensor readings, such as fields introduced by the human hand or otherelectronic circuits nearby. The conductive ground pad 36 and thegrounded conductive cone 22 also protect the sensing electrodes 30 andtheir associated electronics from high voltage electric discharge.

In a preferred implementation of the sensor of FIGS. 2 and 3, the outerdiameter of the sensing electrodes 30 and the base (top) of theconductive cone 22 are both 1 cm, and the wire 32 is 0.61 mm diameter.The implementations made by the inventor have used steel piano wire, andother types of music wire, such as strings for stringed instruments, mayalso be used.

Changes in capacitance are preferably measured by incorporating each ofthe sensing electrodes 30 into a respective RC oscillator. The resultantRC time constant, and therefore the frequency of oscillation, is afunction of the capacitance between the conductive cone 22 and therespective sensing electrodes 30.

Referring now to FIG. 4, there is presented an electrical schematic of apreferred embodiment of circuitry for utilizing the capacitancesprovided by the apparatus of the invention.

The four sensing electrodes 30 of FIGS. 2 and 3 are represented in FIG.4 as variable capacitors Ca, Cb, Cc, and Cd. The ground of each of thesensing electrodes 30 is preferably that of the conductive cone 22.

The variable capacitance values are used in combination with feedbackresistors R8, R3, R4, and R9, and with NAND gates U1/A, U1/B, U1/C, andU1/D (preferably provided in a 74HC132 Schmitt-triggered inputintegrated circuit; pinouts shown), to create four oscillators and asensor selector.

Each NAND gate has two inputs, one serving as an oscillator input (e.g.,the pin 2 input of the U1/A gate of the 74HC132 device, which is shownas coupled to the sensing electrode 30 represented as the capacitor Ca),and the other (e.g., the pin 1 input of the U1/A gate) serving as aselection control line. When the selection control line of one of thefour NAND gates is high (the other three control lines being low), theselected oscillator will oscillate.

The outputs of the four NAND gate oscillators (e.g., pins 3, 6, 8, and11 of the illustrated 74HC132 device) are ORed together by a transistorQ5 (e.g., a 2N3906 PNP bipolar transistor). Suitable coupling, such asresistors R7, R2, R5, and R10, are provided. The output of thetransistor Q5 (the collector of the transistor Q5) thus produces asignal which oscillates at a frequency related to the capacitance of theselected sensing electrode 30.

The frequency of oscillation of the ORed result is counted by amicrocontroller 38, preferably a PIC16C58A integrated circuit (pinoutsshown). The microcontroller 38 runs calibration code that normalizes thegain of each of the four illustrated sensor circuits, producing anormalized force signal, compensating for component, mechanical, andmanufacturing tolerances.

Since the sensor is to emulate a conventional mouse pointing devicewhich has velocity as an output, the microcontroller 38 performs anon-linear transformation on the normalized force signals to produce avelocity signal. The microcontroller 38 formats the velocity signal intoconventional mouse protocol such as “Microsoft Mouse”, and sends thevelocity signal out through an output such as a serial port (RS-232 orPS/2) 39, or an infrared (IR) port 37.

In the embodiment of FIG. 4, two types of communication interfaces,infrared (IR), generally shown as 37, and wired, generally shown as 39,are provided. Either or both may be used in implementations inaccordance with the invention.

In the IR interface 37, a high current transistor Q6 (e.g., an FZT869)switches high-brightness infrared light emitting diodes 37A (e.g.,HSDL4220) for infrared communication. In the wired interface 39, a lowcurrent switching transistor Q4 (e.g., 2N3906) implements a serialRS-232 communication interface 39A.

In a preferred embodiment, the microcontroller 38 selects one of theNAND gate oscillators, and counts the number of oscillations for a fixedperiod of time. The final count is proportional to the sensor frequency80, and is used to determine the applied force. This will be explainedin greater detail in the section “DYNAMIC CALIBRATION”, appearing below.

The feedback resistors R8, R3, R4, and R9 are chosen for the maximumoscillation frequency countable by the microcontroller 38, typicallyless than 1 MHZ. Each sensor channel is integrated (oscillation counted)for 2.5 msec, resulting in a 100 Hz update rate of force direction andmagnitude applied to the conductive cone 22. The implementation providesa 10 bit resolution sensor measurement signal with a full-scale changein excess of 25%.

The current cost for large quantities (e.g., more than 100,000) of theSchmitt-trigger NAND circuits, and of the microcontroller 38, isapproximately $0.20 and $1.00 per piece, respectively, making itpossible to construct a capacitive sensor with acquisition andprocessing hardware for less than $3. These figures compare quitefavorably with previous implementations of pointing devices, such asthat of co-pending patent application Ser. No. 08/181,648. Note alsothat the other conventional devices, such as that shown in the Hughespatent, would evidently be much more costly to produce, even if theywere suitable for in-keyboard applications.

Compared with Hughes, devices according to the invention are easier andless expensive to fabricate, using a conventional printed circuit boardprocess, and are more compact because they have a lower profile.

Attaching the articulating member 20 to the two dimensional surface(such as the circuit board 28) which includes the sensing electrodes 30,as shown in FIGS. 2 and 3, decreases material and assembly cost, andmakes for a more compact device.

Note, also, that the prior art Hughes patent teaches a device whosequiescent position places no conductor in the vicinity of the sensingelectrodes. In that quiescent position, each of the capacitances of eachsensing electrode is negligible, due to the relatively great distance.By contrast, in the present invention, the conductive cone 22 is in thevicinity of the sensing electrodes 30. The capacitances of the sensingelectrodes 30, in the quiescent position, have finite, measurable, anduseable values.

Moreover, the quiescent capacitance values need not necessarily be equalor even substantially equal. As will be discussed below, transferfunctions, including scaling, are employed to utilize the rawinformation obtained from the capacitance values.

Because the invention employs a plurality of sensing electrodes, such asthe exemplary four two-dimensional sensing electrodes 30, are disposedon a substrate in continuous close proximity to the articulating member20, necessitates calibration unforeseen by Hughes. The present inventionprovides calibration to create an accurate and sensitive force sensorfrom low-cost, low tolerance parts, using low-cost constructiontechniques. Measuring small forces accurately near the quiescentposition is vital for pixel manipulation in computer applications. Thus,even taking into account the manufacturing time and costs associatedwith the calibration, the resultant sensor according to the inventioncompares favorably with conventional devices.

The capacitances are calibrated, preferably by using an adaptivealgorithm in which the maximum, minimum, and quiescent channel readingsare stored, and in which a gain factor is calculated from these values.Independent RC oscillators are used, each sensing electrode 30contributing substantially to the capacitance of one RC oscillator.Therefore, advantageously accurate values are obtained.

Second Embodiment

Sensing Device with Select Switch

In accordance with a second embodiment of the invention, a switch isprovided, along with the sensing apparatus described above. The switchis preferably monostable, having a stable position when the articulatingmember 20 is not being manipulated, and having a second position, whichthe switch enters when the articulating member 20 is manipulated in asuitable fashion, and remaining in the second position only until theuser ceases manipulating the articulating member 20.

The switch is provided for either (or both) of two purposes. The firstpurpose is related to the use of mechanical switches, on conventionalmice, to select objects (one click), to launch programs (two clicks),and to select and drag an icon or other object (press to select object,hold while moving object). A switch as provided in the embodiment to bedescribed provides for that same functionality.

The second purpose of the switch of the present embodiment has to dowith power savings. In battery powered systems, such as portablecomputers and audio/visual equipment remote controls, the sensorelectronics are preferably powered only when the sensor is actuallybeing used by an operator. Switching is provided, in accordance with theinvention, to achieve this power savings.

Power savings is implemented as follows: A timer is used to shut off thesensor electronics after a period of inactivity. In an embodimentsimilar to that of FIG. 4, the microcontroller 38 is preferablyprogrammed to perform the timing and switching function.

To re-activate the sensor electronics, the switch is used to indicateuser activity. In a preferred implementation, a polling scheme is used.In such a scheme, the sensor electronics are periodically energized, forexample every second, to check for activity. When the polling indicatesthat the sensor has been touched, power is restored. Touching ispreferably detected by means of a threshold pressure, such as 10 grams.Closing the switch sends a “wake up” signal to the microcontroller 38.

In a preferred way of enabling such a switching arrangement to wake upthe microcontroller 38, the user applies a vertical (z axis) force tothe pointing stick, achieved through the embodiments described below.(Note, by the way, that similar user manipulation of the deviceaccording to the invention may also select and drag an object.)

Referring to FIG. 5, a mechanical switch 50 is placed underneath thesensor, offset from the articulating member 20, using the circuit board28 as a lever arm, and having a fulcrum 52 disposed across from theswitch 50. The location of the fulcrum 52, the member 20, and the switch50 may be positioned, relative to each other, in any suitablearrangement to obtain the desired activation force and displacement.

The mechanical switch 50 is preferably a metal dome type, to givetactile feedback (an impulse “click”) when engaged, and hysteresis whendisengaged. The switch activation force should preferably be greaterthan the force used to move a cursor, to prevent accidental switchengagement when translation of the cursor was intended. A typical switchactivation force is 350-400 grams with 50 grams of hysteresis.

Referring to FIG. 6, an articulating member 59 is used in place of theconductive cone 22. The upper surface of the member 59 has a shape andtexture suitable for good contact with a user's fingertip, and is notessential to the invention. In a preferred embodiment, the member 59 ismade of molded rubber. However, other materials, having propertiessuitable for the purpose to be described herein, may be used.

The lower surface of the member 59, which faces the sensors 30, hasdisposed thereon a conductive layer, such as a layer of conductiverubber 58. The conductive rubber layer 58 preferably has a shallowconical shape, to provide a variable gap between the conductive rubber58 and the sensing electrodes 30. As shown in FIG. 6, the apex of thecone-shaped conductive rubber 58 is slightly closer to the board 28 thanthe perimeter of the conductive rubber 58 is. This arrangement lendsitself well to calibration (described below).

The member 59 preferably has low resilience. Manipulation by the user'sfingertip causes the member 59, as a substantially rigid body, to bedisplaced. Likewise, the conductive layer 58 is displaced, so as tocause changes in capacitance, similarly to the changes in capacitancedescribed above for the previous embodiment of the invention.

A force applied to the top of the articulating member 59 in the x-yplane (a lateral force, that is, having a component parallel to thecircuit board 28) causes a section of the conductive rubber 58 to movecloser to the sensing electrodes 30. This closer proximity causes adifferential change in capacitance among the four sensing electrodes 30.

A force applied to the apex of the articulating member 59 in the z-axis(straight down towards the circuit board 28) causes the conductiverubber 58 to move closer to all four sensing electrodes 30. This motioncauses a common mode change in capacitance among the four sensingelectrodes 30.

The microcontroller 38 of FIG. 4 processes the four sensing electrodesignals so as to identify this z-axis force. A preferred method of doingso is to sum the calibrated outputs of each sensor channel. Thiscalculation will be discussed in more detail in the section describingcalibration (below).

A switching state can be deduced from the identified z-axis force byseveral techniques. A simple method is to set an absolute threshold thatmust be exceeded to be interpreted as a change in switch state.Hysteresis can be added to prevent switch “chatter” when the z-axisforce, applied to the apex of the articulating member 59, centers aroundthe switching threshold.

Another method is to compare a derivative of the z-axis force with athreshold value. This method can employ the first derivativerepresenting velocity, or the second derivative representingacceleration.

Another aspect of the preferred structure of FIG. 6 provides tactilefeedback. A thin wall 57 is shown, running around a perimeter of thearticulating member 59. The thin wall 57 is shown, in the cross-sectionof FIG. 6, at either outer end of the articulating member 59. The shapeof the wall 57 preferably follows the shape of the perimeter of thearticulating member 59. Where the member 59 is cone-shaped, the wall 57is annular in shape, similar to that commonly provided in rubber domeswitches.

As per similar structures in dome switches, this wall 57 provides a“breakaway force. That is, an abrupt tactile sensation, responsive tofingertip force of a suitable magnitude, is caused by the collapse ofthe thin wall 57 under the pressure from the users fingertip.

The breakaway force provides physical tactile feedback to the user whenthe articulating member 59 is pressed in the z-axis with sufficientactivation force (e.g. 30 grams). For the purpose of operating the GUI,the circuitry of FIG. 4 detects the activation force as a dramaticchange in the sum of all sensor channels by the microcontroller 38.

In another preferred embodiment, a switch sensing electrode 56 isprovided on the circuit board. (FIG. 6 shows the electrode 56 centeredbelow the articulating member 59, but other suitable locations may alsobe used.)

The collapse of the thin wall 57 allows the conductive rubber 58 to makephysical resistive contact with the switch sensing electrode 56, closingan electrical circuit and generating an electrical signal. The electricsignal can be used to wake up the microcontroller 38 from its sleepingmode, or to function as a mouse switch (e.g. to select an object) whenthe microcontroller 38 is operating.

The embodiment illustrated in FIG. 6 may be built using otherwiseconventional rubber dome switch materials and otherwise conventionalmanufacturing techniques, minimizing cost and complexity. Thearticulating member 59 and the conductive rubber 58 can be part of a onepiece multiple switch assembly, such as those used on television remotecontrols. Some alternative methods of manufacture include coating theside of the articulating member 59 facing the circuit board 28 with aconductive material, or impregnating the entire articulating member 59with a conductive filler, such as carbon.

Third Embodiment

Resilient Conductive Material

Another preferred embodiment of the apparatus of the invention is shownin FIGS. 7A, 7B, and 7C, a general cross-sectional view and two detailedcross-sectional views, respectively.

Referring to FIG. 7A, an articulating member 60 is disposed on thecircuit board 28, the latter having the sensing electrodes 30 and theswitch sensing electrode 56 disposed thereon, as per previouslydiscussed embodiments. The conductive rubber layer 58 of FIG. 6 isreplaced by a textured conductive rubber 62, attached as before to theinside (lower) surface of the articulating member 60.

A thin insulating layer 63 (e.g., solder mask or non-conducting tape) ispreferably provided, to prevent resistive contact between the conductiverubber 62 and the sensing electrodes 30.

FIGS. 7B and 7C are views of surface detail of the textured conductiverubber 62. As shown in FIG. 7B, the surface includes alternatingprojections 61, preferably in the form of teeth, and voids 64.

As shown in the detail of FIG. 7C, when force is applied to thearticulating member 60, the conductive rubber 62 compresses against thecircuit board 28. This causes the teeth 61, made of resilient,conductive rubber material, to deform and expand sideways, filling thevoids 64.

The deformation of the conductive material brings more of the conductivematerial closer to the sensing electrodes 30. This added proximitydecreases the capacitance between the conductive rubber 62 and thesensing electrodes 30.

Fourth Embodiment

Floating Conductive Cone

A fourth embodiment of the invention is shown in a cross-sectional viewin FIGS. 8A and 8B. As is the case with previously described embodimentsof the invention, the conductive cone 22 is suspended above the sensingelectrodes 30 by the articulating member 20.

In this embodiment, however, the articulating member 20 includes a shaft24, preferably oriented along a vertical axis, and having a top 26 foruser fingertip manipulation. Also, an immobile support member 35 iscoupled to the shaft 24 by a flexible member 132. Preferably, theflexible member 132 has a convex shape similar to that of a collapsibledome, so that user manipulation can cause a collapse of the flexiblemember 132, the collapse providing tactile feedback. The support member35 is preferably annular, as shown in FIG. 8B, and preferably has aplurality of anchoring posts 37, which are inserted into apertures inthe board 28, to anchor the support member 35 in place.

The cone 22 is coupled to the bottom of the shaft 24, to move therewith,responsive to user fingertip manipulation. As before, narrow gaps 33exist between the surface of the cone 22 and the sensors 30.

Forces normal (x and y) and parallel (z) to the shaft 24 may be measuredby the illustrated apparatus. The gaps 33 between the entire conductivecone 22 and the electrodes 30 (typically 0.01 inch at zero force), incombination with the articulating member 20, allow three dimensionalmovement of the conductive cone 22 by forces applied to the shaft 24.The flexible member 132 provides the restoring force, and is preferablyshaped as an arch, to distribute the stress and keep the stress wellwithin the elastic limit of the material. The thickness of the flexiblemember 132, the length of the shaft 24, and the modulus of the materialcontribute to the sensitivity and maximum force that can be measured.

A typical articulating member 20, constructed of nylon with a 0.4 inchlong shaft and a 0.01 inch wall flexible member 132, can operate overone million cycles when flexed with a 350 gram load.

The present embodiment of the invention offers advantageously simpleconstruction and installation. The anchoring posts 37 are preferablymade of a material, such as nylon, which can be ultrasonically welded tothe circuit board 28. The conductive cone 22 and articulating member 20are preferably injection molded parts, press-fit together. The cap 26preferably has texturing, such as protrusions molded into the part(preferably less than 0.005 inch in width and 0.01 in length), to catchthe skin of the finger, providing a “grippy” high friction top.

This embodiment facilitates reduction in the use of conductive material,which often costs more than non-conductive materials. Preferably, theconductive cone 22 is made of conductive plastic (for example, 50%carbon fiber filled nylon, part number #J-1/CF/50/EG from DSMEngineering Plastics, Evansville, Ind.), and the articulating member 20is made of non-conductive nylon.

In a preferred embodiment of the invention, inactive electrodes 30(non-selected, non-oscillating) provide enough proximal ground referenceto the conductive cone 22, eliminating the need for an electricalconnection to the conductive cone 22. In another embodiment, theconductive cone 22, the underside of the flexible member 132, andsurface of the anchor posts 37, are made of conductive material (forexample, carbon filled polymer thick film conductive paint, part #7101,Dupont Electronics, Research Triangle Park, N.C.), to provide a lowimpedance (e.g. under 1,000 ohms) to the conductive ground pad 36,increasing the dynamic range, electronic shielding, and noise immunityof the invention.

Preferably, the embodiment of FIGS. 8A and 8B hermetically seals theelectrodes 30 from the environment, providing a barrier from moisture(humidity) and other contaminating matter. Referring to FIG. 8B, a topview of the embodiment, the annular rim 35 completely seals theelectrodes 30 from the environment.

Dynamic Calibration

Yet another aspect of the present invention is that of an algorithm,used in conjunction with the above-described apparatus, to compensatefor component, manufacturing, thermal, humidity, mechanical, and supplyvoltage variability. The algorithm runs during operation of a systemincorporating the invention, and may be implemented in program code, tobe executed by the microcontroller 38 or by a system CPU (not shown).

FIG. 9 is a graph, showing sensor frequency 80, such as that produced bythe microcontroller 38 of FIG. 4, versus force 82 applied to a deviceaccording to the invention by a user's fingertip. The graph pertains toa capacitive link between an articulating member and one of the sensors(see any of the above-discussed embodiments. It will be understood that,for a device employing a plurality of sensors, such as those shown inFIG. 3, there will be a separate such curve for each of the sensors.

The applied force (the abscissa of the graph) has a neutral, centralpoint at which zero force is applied. Deviations from the zero point, inthe horizontal direction, reflect either tension 86 or compression 83,caused by opposite-direction forces applied to a given one of thesensors 30.

The frequency 80 of a sensor channel decreases as the conductive cone 22is forced towards a sensing electrode 30 (COMPRESSION 82). When theconductive cone 22 is pulled away from a sensing electrode 30 (TENSION86), the capacitance is decreased, and hence the frequency increases.The domain of force values is bounded by MAX and MIN applied forcevalues, shown in this example as being plus and minus 400 grams.

The sensor frequency output is a force-to-frequency curve, which, forthe present example, is marked as RAW 88, the “RAW” referring to thefact that the curve has not yet been subjected to the algorithm(discussed below). The curve 88 has three points, CENTER 90, MAX 92, andMIN 94, which define the sensor frequencies for the zero, MAX, and MINapplied force values. The force-to-frequency curve 88 runs between thesepoints. The points, i.e., their coordinates according to the abscissaand ordinate, are stored, as reference values, for each sensor channel.

The shape of the force-to-frequency curve 88 depends on several factors,including the geometry of the articulating member 20 and of the sensingelectrodes 30. The curve need not be linear, and it is contemplated thatfor most implementations of the above-discussed apparatus, it will notbe so. For the geometry illustrated in FIGS. 2 and 3, the curve isnon-linear.

The calibration algorithm acts to modify, preferably to linearize orpiecewise linearize, the force-to-frequency curve 88. The algorithmconverts the curve 88, given in terms of the ordinate scale on the leftside of the graph, into a calibrated sensor force 102, given in terms ofanother ordinate scale on the right side of the graph. The range of thecalibrated sensor force 102 runs between a minimum 104, labeled−RANGE,and a maximum 106, labeled+RANGE 106. The minimum 104 and the maximum106 are shown having normalized values −64 and +63, respectively.

The preferred calibration algorithm approximates the non-linear curveRAW 88 as two linear segments, running between the points 90, 92, and94. These segments have slopes shown as SCALE_TENSION 96 andSCALE_COMPRESSION 98. The slopes are calculated between the maximum 92,the minimum 94, and the center 90 points, as shown.

In a preferred embodiment, the MAX 92 and MIN 94 reference values aredynamically updated every time a sensor channel is read. This typicallyhappens 100 times per second. The CENTER 90 is updated when thearticulating member 20 is undisturbed, that is, when no external forceis applied.

In one embodiment, an undisturbed state is declared when the changes inthe calibrated sensor outputs 102 of all of the sensor channels remainwithin a minimum movement tolerance for a fixed period of time, forexample, when the changes all remain within three calibrated units,according to the sensor output 102 scale, for three seconds.

The following is a pseudo-code representation of the preferredcalibration algorithm performed for each sensor channel value:

RAW 88 = new sensor reading if (RAW 88 > MAX 92) MAX 92 = RAW 88 else if(RAW 88 < MIN 94) MIN 94 = RAW 88 if MAX 92 or MIN 94 has changed, dothe following { if (RAW 88 > CENTER 90) SCALE_TENSION 96 = +RANGE 106/(MAX 92-CENTER 90) else if (RAW 88 < CENTER 90) SCALE_COMPRESSION 98 =−RANGE 104/ (CENTER 90-MIN 94) } if (RAW 88 > CENTER 90) CALIBRATED 101= SCALE_TENSION 96* (RAW 88-CENTER 90) else if (RAW 88 < CENTER 90)CALIBRATED 101 = SCALE_COMPRESStON 98* (CENTER 90-RAW 88)

Once the calibrated sensor output (given in terms of the calibratedsensor force scale 102) are obtained for each sensor channel, thecalibrated values are subjected to a force-to-velocity transferfunction. A preferred transfer function is described in the IBMEngineering Specification Integrated Pointing Device EngineeringSpecification: Pointing Stick Type”, by T. Selker, J. Rutledge, and B.Olyha, May 17, 1994, pg. 22.

In a preferred embodiment, the calibration reference values (the slopedline segments SCALE_TENSION 96 and SCALE_COMPRESSION 98, and the pointsMAX 92, MIN 94, and CENTER 90) are measured and calculated dynamically.In another embodiment, the calibration reference values are stored inEEPROM or ROM during manufacture.

An implementation of the dynamic calibration algorithm, transferfunction, and additional code to perform serial mouse protocol andinfrared wireless modulation occupies less that 2K of ROM and 72 bytesof RAM in the PIC16C58 microcontroller 38.

It is an objective of the invention to operate reliably on batterypower. The frequency of the NAND RC oscillators is dependent on supplyvoltage. The voltage of alkaline batteries decreases as energy is drawn.A preferred embodiment uses a zener diode to stabilize the supplyvoltage to the NAND circuit. Another embodiment periodically decrementsthe MAX 92 and MIN 94 value, by a fixed increment, to track the decreasein oscillation frequency.

The non-linearity of the force-to-frequency curve (the curve shown inFIG. 9) of the devices according to the invention, such as that of FIG.2, can be minimized by reducing the range of deflection of theconductive cone 22, preferably by increasing the stiffness or diameterof the wire 34. A smaller deflection range spans a smaller section ofthe RAW 88 curve, which is more closely approximated by a linear fit.

In one embodiment, a sensor constructed with a 0.4 inch diameter cone22, cone angle of 6 degrees, 0.024 inch diameter music wire 32, and anoverall length (i.e., height to the top of the cap 26) of 0.5 inches,resulted in a calibrated sensor output 102 which is linear to within 6%.The accuracy of the piece-wise linearization technique can further beenhanced by increasing the number of calibration samples.

In another embodiment, the shape of the RAW 88 curve is linearized bythe particular shape of the sensing electrodes 30. Referring to FIG.10A, the sensing electrodes 30 are concave-tapered to decrease the slope(sensitivity) of the frequency output 88 around the quiescent (zeroforce) region. Referring to FIG. 10B, the sensing electrodes 30 areconvex-tapered to decrease the slope of the frequency output 88 aroundthe MAX 92 and MIN 94 region. Decreasing the area of the sensingelectrodes 30 decreases the dynamic range of the sensor 21. If thedynamic range, for a given configuration of the electrodes 30 is notadequate for a particular application, then the dynamic range can berecovered by increasing the diameter of the cone 22.

The above described embodiments are intended to illustrate theprinciples of the invention, but not to limit its scope. Otherembodiments and variations to these embodiments will be apparent tothose skilled in the art, and may be made without departing from thespirit and scope of the invention as defined in the following claims.

What is claimed is:
 1. An apparatus for sensing manipulation by a userand for producing signals related to the manipulation in X and Ydirections, the apparatus comprising: an articulating member whicharticulates responsive to user manipulation thereof, the articulatingmember including an electrically conductive member; a planar member; aplurality of sensing electrodes disposed in parallel to the planarmember and about the articulating member to face the electricallyconductive member of the articulating member, whereby respectivecapacitances exist between the electrically conductive member andrespective ones of the sensing members, the capacitances having valueswhich vary related to articulation for the articulating member;detection means for each sensing electrode for detecting respectivecapacitances and for outputting articulation signals responsive to thedetection of the respective capacitances; and calibration means appliedto individual articulation signals for providing a unique scaling valuefor each articulation signal, wherein the scaling value is calculatedfrom a set of reference values at least one reference value for eachsensing electrode, that are dynamically updated.
 2. An apparatus asrecited in claim 2, wherein the articulating member includes: ananchoring member rigidly coupled to the planar member; a movable memberwhich is movable responsive to user manipulation thereof; and a couplingmember, physically coupled between the anchoring member and the movablemember, the coupling member being flexible to allow movement of themovable member relative to the anchoring member.
 3. An apparatus asrecited in claim 2, wherein: the anchoring member is annular in shape;and the coupling member is shaped so as to have a quiescent position anda collapsed position, a physical transition between the quiescentposition and the collapsed position providing a user with tactilefeedback.
 4. An apparatus as recited in claim 3, wherein the couplingmember is one of (i) dome-shaped and (ii) shaped as an annular arch. 5.An apparatus as recited in claim 1, further comprising a switch having afirst position when the articulating member is not being manipulated,and having a second position, entered when the user manipulates thearticulating member.
 6. An apparatus as recited in claim 5, wherein thearticulating member includes a collapsible member having collapsed andnon-collapsed positions, the collapsible member entering the collapsedposition responsive to user manipulation of the articulating member, andremaining in the non-collapsed position otherwise.
 7. An apparatus asrecited in claim 1, wherein: the apparatus further includes aninsulating, dielectric layer disposed on the planar member rover thesensing members; and the electrically conductive member of thearticulating member includes a resilient layer of electricallyconductive material, the layer having a textured surface includingprojections and voids; whereby, responsive to manipulation of thearticulating member, the projections make contact with the insulatinglayer to establish a capacitive link with the sensing members; andwhereby, responsive to further manipulation of the articulating member,the projections in contact with the insulating layer are deformed so asto increase a quantity of the electrically conductive material of theresilient layer which is in contact with the insulating layer, therebychanging a capacitance value of the capacitive link.
 8. The apparatus ofclaim 1, wherein the sensing electrodes each comprise shapes so as toproduce desired transfer functions between articulation of thearticulating member and the values of the articulation signals.
 9. Theapparatus of claim 8, wherein the sensing electrodes each comprise ataper of increasing area.
 10. The apparatus of claim 8, wherein thesensing electrodes each comprise a taper of decreasing area.
 11. Theapparatus of claim 1, wherein the apparatus further senses manipulationin the Z direction and individual articulation signals are summed toproduce a signal representing the Z direction component of force appliedto said articulating member.
 12. The apparatus of claim 1, furthercomprising means applied to individual articulation signals forproviding a quiescent value for each articulation signal indicating theuser has ceased manipulation of the articulating member.
 13. Theapparatus of claim 1, further comprising switch means for receiving aforce applied to the articulating member and an output for providing aswitch activation signal.
 14. The apparatus of claim 13, furthercomprising: wake-up means for receiving switch activation signal and forproviding a wake-up signal; and a microprocessor with at least a normalpower mode and low power mode, whereby when said microprocessor is inlow power mode, said wake-up signal causes said microprocessor to leavethe low power mode and enter into the normal power mode.
 15. Theapparatus of claim 13, wherein said switch means comprise a mechanicalswitch.
 16. The apparatus of claim 13, wherein said switch means furthercomprise an electrical contact disposed on the planar, whereby contactbetween the electrically conductive member of the articulating memberand said electrical contact occurs when a force is applied to thearticulating member.
 17. The apparatus of claim 1, wherein said detectormeans includes an oscillator circuit, whereby the frequency of theoscillator is dependent on the value of the respective capacitance,further comprising selection means to sequentially enable eachoscillator in a temporal sequence.
 18. The apparatus of claim 1, furthercomprising switch means for receiving a force applied to thearticulating member and an output for providing a switch activationsignal.
 19. The apparatus of claim 18, further comprising: wake-up meansto receive switch activation signal and output a wake-up signal; and amicroprocessor comprising at least a normal power mode and a low powermode, whereby when said microprocessor is in the low power mode, saidwake-up signal causes said microprocessor to leave the low power modeand enter into the normal power mode.
 20. The apparatus of claim 18,wherein said switch means comprise a mechanical switch.
 21. Theapparatus of claim 18, wherein said switch means comprise an electricalcontact disposed on the planar, whereby contact between the electricallyconductive member of the articulating member and said electrical contactoccurs when a force is applied to the articulating member.
 22. Anapparatus for sensing manipulation by a user and for producing signalsrelated to the manipulation in X and Y directions, the apparatuscomprising: an articulating member which articulates responsive to usermanipulation thereof, the articulating member including an electricallyconductive member; a plurality of sensing electrodes disposed about thearticulating member to face the electrically conductive member, wherebyrespective capacitances exist between the electrically conductive memberand respective ones of the sensing electrodes, the capacitances havingvalues which vary related to articulation for the articulating member;calibration means applied to individual articulation signals to providesa unique scaling value for each articulation signal, wherein saidscaling value is calculated from a set of reference values, at least onereference value for each sensing electrode, that are dynamicallyupdated; and an oscillator circuit for each sensing electrode, whereinthe frequency of the oscillator is dependent on the value of therespective capacitance, selection means to sequentially enable eachoscillator in a temporal sequence.
 23. The apparatus of claim 22,wherein the sensing electrodes each comprise shapes so as to producedesired transfer functions between articulation of the articulatingmember and the values of the articulation signals.
 24. The apparatus ofclaim 23, wherein the sensing electrodes each comprise a taper ofincreasing area.
 25. The apparatus of claim 23, wherein the sensingelectrodes each comprise a taper of decreasing area.
 26. The apparatusof claim 23, further comprising calibration means applied to individualarticulation signals for providing a quiescent value for eacharticulation signal indicating the user has ceased manipulation of thearticulating member.
 27. The apparatus of claim 22, wherein the scalingvalue is calculated from a set of reference values, at least onereference value for each sensing electrode, that are dynamicallyupdated.
 28. The apparatus of claim 22, further comprising switch meansto receive force applied to the articulating member and output a switchactivation signal.
 29. The apparatus of claim 28, further comprising: awake-up means for receiving a switch activation signal and for providinga wake-up signal; and a microprocessor with at least a normal power modeand low power mode, whereby when said microprocessor is in low powermode, said wake-up signal causes said microprocessor to leave the lowpower mode and go into normal power mode.
 30. The apparatus of claim 28,wherein said switch means comprise a mechanical switch.
 31. Theapparatus of claim 28, wherein said switch means further comprise anelectrical contact disposed on the planar, whereby contact between theelectrically conductive member of the articulating member and saidelectrical contact occurs when a force is applied to the articulatingmember.
 32. The apparatus of claim 22, wherein the sensing eachelectrodes comprise shapes so as to produce desired transfer functionsbetween articulation of the articulating member and the values of thearticulation signals.
 33. The apparatus of claim 32, wherein the sensingelectrodes each comprise a taper of increasing area.
 34. The apparatusof claim 30, wherein the sensing electrodes each comprise a taper ofdecreasing area.
 35. The apparatus of claim 22, wherein the apparatusfurther senses manipulation in the Z direction and individualarticulation signals are summed to produce a signal representing the Zcomponent of force applied to said articulating member.
 36. Theapparatus of claim 22, further including calibration means applied toindividual articulation signals for providing a quiescent value for eacharticulation signal indicating the user has ceased manipulation of thearticulating member.